Secrecy system of radio broadcast distribution



Dec. 11, 192s. '1,695,180

E. E'. CLEMENT SEGRECY SYSTEMOF RADIO BROADCAST DISTRIBUTION Original Filed May 21, 1925v 5 Sheets-Sheet 1 im? En,

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E. E. CLEMENT SECRECY SYSTEM 0F RA\DIO BROADCAST DISTRIBUTION Original Filed May 21', 1925 5 Sheets-Sheet 2 E. E. CLEMENT SECRECY SYSTEM 0F RADIO BROADCAST DISTRIBUTION Dec. 11, 192s. 1,695,180

original Filed May 21, 1925 5 sheets-sheet 3 Dec. 11, 1928.

E. E. CLEMENT SECRECY SYSTEM OF RADIO BROADCAST DISTRIBUTION m L1 vL ,iil

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E. E. CLEMENT SECRECY SYSTEM' OF RADIO BROADCAST DISTRIBUTIN Original Filed May 21, 1925 5 Sheets-Sheet 5 DEPATCH SHEET sTATlON "A" UATr.

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SHEET :mman B DURATION REMARKS "E" DNISION N.' REMAZKS Patented Dec. 11.1, 1928.

UNITED sTAIEsgPATENTLoFFlcE.

iimivARn E. CLEMENT,v OF WASHINGTON, DISTRICT or COLUMBIA, ASSIGNOR To EDWARD F. OOLLAIIAY/y OF WASHINGTON, DISTRICT OF OOIMIIRIA SECRECY SYSTEM OF RADIO BROADCAST DISTRIBUTION.

Original application led May 21, 1925,

Serial NO..Y31,928. Divided vvand this appliiation led October 80,

1925. Serial No. 65,861.

subdivision of the ultimate units or subscribers stations into localgroups in local areas, each group related to a local or regional distributing station;- the grouping of these regional stations according to districts and relating each district group of regional stations to a district master station; the grouping of istricts into divisions, which may conveA ien ly coincide with the geographical stan ard time divisions ofv thev country; and finallyA the relation of the district master stations to a central master station.

There .may be more intermediate steps or stations interposed between the subscribers control or regional station and the central master station and there may be direct connection between the said regional stations and the central master station, but these.

possible variations will be apparent from the detailed description and do not change the principleinvolved, In any case, for purpose of distribution, the central master station broadcasts to the district master stations on district carrier wave frequencies, each of the district master stations broadcasts to its constituent regional central stations on a fixed carrier wave frequency, permanently.

l` and transmitting instruments at eachof the allotted thereto, and each local or regiona central station broadcasts to the subscribers in its local area on ac'ommon fixed carrier wave frequency permanently allottedtheret local or regioilal distributing stations C;

.to the smallest station. 'In oher Thu's it will be apparent that the first characteristic feature of the method is thatl of sending from each center to the class or Aand the subscribers instruments in general D,`then we may say that A transmits to B on B frequency, B transmits to4 C on C frequency, and C transmits to D on D free quency, Of the respective carrier waves. For information that goes through from A to D, or that goes through from B te D, as well as information originating with C, the original. modulations are actually reproducedy in the -instrumen'ts at D,- by'means which will be described. The simplest way to do l this is by double modulation, which also enables easy change of primarycarrier wave frequency at the intermediate or relaying -stations'without changing the intermediate carrier frequency, whereon and whereby the original modulations are preserved By contemplated to have national, district and local programs made up day by day, from which any subscribers may select. Selection by the subscriber is determined by frequencies, which by the use Ofdouble modulation may be frequencies ofthe envelope or intermediate wave transmitted.

The great benefitof double modulation as will be hereinafter pointed out, is that a great range of selection can thereby be af.-

forded any lo'c'al station and any local ex-` change, which will be the Vsame for all partsl of the country and for every exchange down hamlet, or the most distant words, every subscriber in this system may have .access to the. entire program available to` any other subscriber without regard to location, distance, time or circumstances. For this purpose it will be necessary to provide a plurality of receiving means that will be described, itis relay stations to be described, whereby any .which my invention may be practiced 1s illustrated inthe accompanying drawings,

in Which' Fig. 1 shows ,symbolically an arrangement.

and transmit tems -of double modulating and transmitting equipment at the A or master station of the system for matter original there.

A,F ig. 2 shows symbolically equipment for the B stations, by means of which the primarycarrier waves transmitted from the apparatus of Fig. 1 may be demodulated and the intermediate frequency Waves or envelope modulated upon a new carrier wave C.

Fig. 3 shows symbolically apparatus similar to that in Fig. 2, but intended to be located at the local or regional distributing stations C, receiving, therefore, on the C wave frequency, transmitting on the D or subscribers frequency.

Fig. 4 shows symbolically a subscribers set adapted to receive on the D frequency, to demodulate the short carrier wave, and then to demodulate the intermediate frequency carrier wave, so as to produce audio waves as its output.

Fig. 5 is a circuit diagram of a subscribers receiving set arranged for selection through double modulation.

Fig. 6 is a circuit diagram of a subscrib ers receiving set with fixed selective circuits.

Fig. 7 is a view indicating the general outside .appearance of a receiving set having the circuit of Fig. 6.

Fig. 8 is a view indicating the outside'appearance of an amplifier and loud speaker unit. for use with the set :of Figs. 6 and- 7.

Fig. 9 is a circuit diagram of a further simplified form of the subscribers receiving set using two tubes only.

Fig. 10 is a further modification of a subscribers set using separate sets of batteries for each of the two tubes.

Fig. 11 is a modification of the receiving set of Fig. 10 using the fourth or special,-

adjustable filter circuit for the vsecond detector.

Figs. 12, 13, and 14 show the daily; dispatch sheets for the master station, a B statlon, and a C station respectively.

Fig. 15 is a schematic diagram of a relay circuit for combined secrecy and public broadcast service.

Referring now to Figs. 1 to 4 inclusive, and turning to Fig. 1, I have shown therein an arrangement of originating broadcast transmitters which may be'at the head or master station A, or at any other originating station whose program is to-be made available to the subscribers for the time being. The operation is by double modulation, first modulating as by means of a microphone upon a long or intermediate frequency wave, and then modulating the long wave upon a short radio carrier wave of a frequency permanently allotted to and to be received at the stations B. The same arrangement of apparatus will be :found at each of the other central stations through an amplifier toswitch contacts which may be connected through amplifier switch arms to the primary of the transmitter induction coil 302, the secondary of which is connected to the modulator of the generating andv transmitting set. Thus a trunk line or even a subscribers wire may be plugged on to the modulator through the amilifier by means of jack J1. It is to be un'erstood that the function of this transmitting set at any station A, B, or C is primarily to enable local matter to be put into the programs which 'would be by modulating one particular intermediate frequenc or long wave allotted for that purpose. imilarly, each of the stations A, B and C will have its own intermediate frequency for such originating use, and these three or more intermediate frequencies carrying the items originating at the A, i3 and C stations respectively, are normally modulated on the same short carrier wave at each station C and radiated therefrom to its subscribers. The subscribers may then select the items originating at stations A, B, or C, as desired by first detecting ofi' the intermediate frequency waves, and then selecting the articular intermediate frequency desired. y multiplying the number of transmitting andrelc'eiving apparatuses at the several origipating and relay stations, and by enabling each one of them to bring in material over wires and add it to the program, as indicated b jacks J1 and 303 in Figs. 1 and 2, it is o virtus that a very flexible method of operation is rendered ossible, by which each of the smtions A, and C' can determine its own contribution to the nal program which is radiated from station C, and can also sub. stitute if desired items of its own or from other originating stations, for those 1n the regular allotment. This is possible by means of the jack arrangement 303-304, and the multiplication of relays before referred to. This particular feature of m methodwill be further described hereina er.

The function of the apparatus of Fig. 2

frequency allotted to the receivlng station s to take double modulated waves .at the B,vdemodulate the short wave carrier so as to produce the original modulated intermediate frequency waves unchanged from their production in station A, which then without'demodulation are passed through a tuned amplifier 305 to a modulator 306, by means of which they are modulated on a primary or short wave carrier of a frequency suitable for the next lower order of receiving stations, in this case C stations. The short waves thus modulated are then radiated.

By means of the jack 303, intermediate frequency or long waves modulated may be taken off a trunk or off' a jack 304 of another relay set and passed through the amplifier'l 305 to the modulator 306 and thence radiated as before. Also, by means of the jack 304 intermediate frequency or long Waves modulated which have passed through the deinodulator 307 and the amplifier 305 may be forthwith placed upon the Wire trunk lines for transmission to other stations, or may be passed'through the jack 303 of an-v other relay set and thereby carried through the amplifier 305, the modulator 306 and finally radiated on another short carrier wave. These extensions should be available at each stage in the system, and 'I consider it'original with me to providemeans for effecting these combinations of superaudio frequency modulated Waves transmittcd either from wires to'radio carrier or from radio carrier to Wires and thence if desircd back to radio carrier Without change either in the intermediate frequency Waves or in their modulations, and shall claim the same accordingly. This is one essential feature of my present method, which is believed to be original with me and will be claimed l accordingly, i. e., that when 'an originalmodulation is once. made, the wave train carrying that modulation is preserved un.

changed throughout its entire course from point of origin to the listeners ears. As; described herein, I accomplish this by means of` double modulation, with super-audio modulated Waves modulated upon the high frequency radio carrier.

Referring to Fig. 4, this shows typically a subscribers apparatus for taking double modulatedwaves sent out from the stations of any of the preceding there figures, and demodulating the same so as to recover the original audio modulations and make them apparent.' There are two units, one a demodulator of the short carrier wave, whichl produces the long intermediate frequency wave carrying the original audio modulations, and-passes-these to they second demodulator, which'-demodulates the intermediate.

Waves and passes the audio waves to the Ttele'- phone receiver shown at the right of. the figure. This method is shown in detail in my copending application referred to above,

Where vtheV circuit arrangement of such a double demodulator is illustrated in full.

The apparatus shown in Figs. 2 and 3*, is 1` intended to receive a double modulated car- `rier wave such as th t'radiated from the antenna in Fig. l, demodulating the saine and reimpose the long wave or intermediate 150 to the final demodulation bythe intermediate wave demodulator in Fig.A -4, the same intermediate long Wave carrier, and

the same audio modulations thereof, are

maintained intact and unmodified, being merely 'passed alongby relaying from station to station on short carrier Waves, or on wiresas equivalent of the lcarrier Waves.

The apparatus in Fig. 2 and that in Fig.

3 is identical except for the tuning of the transmitted carrier wave.v The description.-

of one therefore will sufce for both.

A simple form of circuit arrangementfor the subsiribers receiving set symbolized-iii Fig. 4, is that shown in Fig. 5. This comprises a receiving antenna 28 coupled to the input circuit of a detectortube 30 having its circuitftuned to the primary wave and a s econddetector tube 31 having its input cirl cuit coupled through a filter coupler 33 'to' the output or plate ycircuit of thefirst dctector 30, the'filter coupler 33 being tu'ed tothe desired intermediate frequency of which there are several, preferably four, carried by the primarywave. subscriber selection of one of `several programsthe filter coupler 33 is arranged to -be tunedl to the different intermediatefrequencies. In the interest of simplifity of control. and uniformity of service, it is desirable tov transmit and receiveone standard primary frequency to which the input circuit of the first detector 30 may set in tune, but Where greater variety and flexibility are desired, the broadcastingmay be done von several primary carrier. waves of different Wave lengths, each carrier being modulated with several intermediate frequency waves. Sich a method of operation will be necessary Where it--is desired to afford subscribers access to the various programs in the different parts of the system. The

To afford the district station B may have a plurality of v relay sets, as already mentioned, and instead of all of 'these setsl having their-input cir- .cuits or wave collectors tuned to the same single radiocarrier frequency, some of them may be tunable to other frequencies in order to pick up other programs, and'in such case the cross connection between jacks 303 and 304 of the diderent sets enable'items from the different programs to be transferred fromone to the other. It is understood of course that filter couplers of any known and Suitable form, which maybe such as that disclosed in Fig. 5, are employed to select the desired intermediate frequency carriers which are to pass through. The second detector 31 of the subscribers set has its output circuit coupled through an audio transformer 34`to the input circuit of an amplifier tube 32 whose output circuit is coupled through a transformer to a loud speaker 36. The usual A and B batteries are provided as indicated at A1 and 13 respectively, the A battery lead 25 being connected to the filament bus 43 through a fila- A ment switch k.

, which, While shown in the drawing as a variable condenser may bey of any suitable form capable of being given a fixed adjustment, instead of the usual wide range variable condense. The output circuit of th'e detector 468 is connected to a pair of intermediate frequencyl bus conductors 473-474 to which the primary side of any of a set of three filter couplers 47 5-476-477 may be connected through different spring contacts 478-479-480 of the program jacks 481-482-483, respectively. The different filter couplers 47 5-476-477 are tuned .respectively to the three dierent intermediate frequencies. Separate second detector tubes, 484-485-5486 are' also provided, one for each -frequency with their input circuits connectedpermanently and .individually to the primary sides of the filter couplers 475-476, respectively. Thus there is a filter coupler, program jack and detector tube for each program.' The individual branches 487- 488-489 of the filament circuits o-f the different tubes are arranged to be connected with the ilament battery supply bus 490 through the spring contacts 491-492-493 of their respective program jacks. The main or central springs of each program jack are connectedin circuit between plates of the detectortubes and the plus, plate battery bus 494( The filament ofthe first detector tube 468 is controlled through a filament switch 495.

In outside appearance the set of Fig. 6

will be generally as indicated in Fig. 7,

that is, with no dials or other variable tuning control devices, the," only apparatus elements appearing on thc face of the.instru ment being the usual aantenna and grouiid binding post, the control button. of the filament switch 495 and thc three program jacks 481-482-483. In connection with this thc telephone headset 496 and cord circuit therefor terminating in a plug 497, is used, the

which may be of any known or other suitable form arranged with the terminals and its input circuit connected With the cord1 and plug connection 500 f-or coupling to 44the receiver set in Fig. 7 through any of the program jacks.

To further simplify the subscribers receiving set, it may be arranged as shown in Fig. 9 where only one second detector tube is used for the several diierent programs instead of one for each program as shown in Fig. 6. In this arrangement onedjack is used and the selection of program is effected through the use of program keys, one for each program. Referring to the circuit arrangement ofFig. 9 in detail, it comprises a first detector 501 having its input circuit 502 adjusted to the standard primary frcquency and its output or plate circuit con-4y nected to the intermediate frequency bus conductors 503-504 which are arranged to be connected with the primary side of any one of the filter couplers 505-506-507 through the contact 508-509 or e510 of the corresponding program key 511, 512, or 513. The second detector tube 514 has its inputs or filament-grid circuit connected to the {ilament grid bus conductors 515-516 to which the primary sides of the filter couplers are arranged to be connected through the contacts 517, 518 and 519 of the respectiv program busses. The common filament ircuit of the first and second detectors is als jointly controlled by the several program keys through the extreme left hand Contact of each which operates upon .closure of the key to connect the common iilament Wire or bus 520 to the minus A battery bus 521. The plate lead 522 of the second detector 514 connects through the common jack 515 to the plus B battery bus 523. As Athe filter couplers 505, 506 and507 are tuned to the three diierent intermediate frequencies carryino as many different programs, the user of121 the set desiring any one program, need only insert the plug of his telephone receiver or loud speaker in the jack 515 and actuate one of the program keys 511, 512 or 513 corresponding to the program desired.

In Fig. 10 the circuit arrangement is the nected in the lament and plate circuits of` the second detector 524 exclusively, while the batteries A11B11 are connected in the filament and plate circuits of the rst detector tube 525 exclusively. It will be noted that to effect the separations of battery supply the only additional wiring and apparatus connections required are tlie common control wires 526 and the extra contacts, one pair in each of the program keys, operable upon actuation of the key to bridge the wires 526 and close the Lcircuit of the fila! ment .of the detector tube 525 through its individual filament battery A11.

In Fig. 11 is shown a modification of the receiving set of Fig. 10 which is the same as that of Fig. 10 except that the fourth filter coupler 527 and program key 528 is provided for the reception of any one of a group of special programs transmitted ony a group of special intermediate frequency waves. the filter coupler r527' differing from the three preceding couplers in that it is arganged to be variably tuned to any one `of the different special wave lengths by the listener,"whichv 1 tuning may be effectedy in any known or suitable manner as by adjustment of the variable condenser shown. Thus for reception of one of the standard programs the subscriber has simply to actuate the program key corresponding to that program andvto receive a special. program Athe key 528 is actuated to connect the special filter coupler 527 in circuit after which it is tuned tothe desired program. This providesmeans in the system enabling a subscriber to make request for a special program to be put on one of the special intermediate frequencies,

so that special programs may be had by certain subscribers without interfering with the regular programs. These special programswoulcl most-usually be programs originating at distant stations and not of general public interest. and for such service the requestingV subscriber will be charged a fee commensurate with the value of the service given. l

To supply the, subscribers with speciali` programs picked Vup. from other stations on a single modulated wave. the relay system o Fig. 15 is provided which consists, as shown, of a detector 529 arranged with its input circuit 530 coupled to a short wave receiving antenna 531 and tuned to receive matter broadcasted on a single modulated wave.' The output circuit of the detector 5.29 is coq)- nected to the input end 'of anv audio amp] iierthe amplified audio output of which is connected through an audio modulator 533 to an intermediate or log-'wave oscillator 534 to modulate the audidlcurren the' long waves produced thereby.. Tllby the detector; 529. By throwing the switch 537 to the left a multiple connection is made from the output circuit of the audio amplier 532 to the audio modulator 538, the output circuit ofwhich'is connected to theshort wave oscillator 536 for direct modulation of the output thereof with the audio waves.' -This results in the primary wave transmitted from the antenna 539 of thel os- @ad of lth, maar 15a! is `@miette cillator 5361 being modulated in, both the audio modulations and the superaudio or long vave modulations which in turn are modulatedwith the same audio modulations, so` that any one with an ordinary re- .ceiver` capable of receiving on the usual single modulated wave may receive the matter being thus broadcasted as well as the/ auth- Thus,l a program or orized subscribers. portions of the program may be donated to the public when sodesired. Switch 537 may vcontrol the connection of the long wave modulator, in a 'manner similar to that of 537, so that either singly or doubly modulated waves can be transmitted -at will. vIt should be noted that by proper adjustment a double demodulatmg receiver can receive single the s stem elastic.

at I claim is: Y

1. A broadcasting system comprising a primary station, a plurality of intermediate relay distributing stations and a pluralty of local receiving stations related to each ,relay station and all in .permanent tune therewith,

vmeans at the primary station for imposingv signal modulations on a wave of'iixedtermediate'frequency, means also at sai tions'for imposing' said modulated termediate frequency wave as a modulation modulation, which makes staupon a high frequency radio carrier wave of-j .fixed frequency permanently alloted to the succeeding relay station or stations, means at said rela station 'to receive said double f modulate waves from the primary station,

means to detect olf. the intermediate frequency waves and to relay and redlstribute the same in its own area by doublemodulation on a primary wave of the standard wave length to which its receiving stations are tuned, means at the local receivingstations: 125" for selecting said programs by first demodulating the high frequency carrier wave received, inorder to strip oifthe intermediate frequency wave or waves and' thereafter selectively detecting the signals modulated-1.y on an intermediate frequency wave, the. said intermediate frequency with its signal modulations being maintained the same from its original modulation at the primary station through the relay station or stations, to and through the subscribers selectors. A

2. The method of radio broadcast distribution which consists in modulating signals on a wave of predetermined and fixed intermediate frequency, then modulating said modulated Wave on a radio carrier wave, also of a predetermined and fixed frequency, relayin the signal modulations by receiving and emodulating the primary carrier wave and reimposing the same modulated intermediate wave Without demodulation on a second radio carrier wave of a ixed and predetermined frequency allotted to the respective relay stations and different from the received frequency, and finally receiving and demodulating said second carrier Wave and thereafter demodulating said intermediate frequency Wave to obtain the signals, said intermediate frequency remainin unchanged from its lirst modulation at t e primary sending station to its nal reception and `lemodulation by the subscriber or ultimate receiver. j

3. The method of radio broadcast distribution which consists in initially modulating signals upon a carrier wave of predetermined and fixed intermediate frequency, then modulating said modulated carrier Wave upon a high frequency radio carrier, and thereafter transmitting said modulated intermediate frequency wave unchanged through one or more relay stations to an ultimate receiver by removing it at each relay station from the radio carrier wave upon which it is received and remodulating it upon a radio carrier Wave of different frequency, and receiving the latter and demodulating it at anultimate receiving station so as to preserve the original characteristics unchanged of both the intermediate fre uency carrier and the signal modulated t ereupon.

In testimony whereof I hereunto aliix my signature. v

EDWARD E. CLEMENT. 

